The present invention in various embodiments relates generally to the useful manipulation of fluorescence found in substrates and particularly most paper substrates as commonly utilized in various printer and electrostatographic print environments. More particularly, the teachings provided herein relate to at least one realization of fluorescence watermarks.
It is desirable to have a way to provide detection of the counterfeiting, illegal alteration, and/or copying of a document, most desirably in a manner that will provide document security and which is also applicable for digitally generated documents. It is desirable that such a solution also have minimum impact on system overhead requirements as well as minimal storage requirements in a digital processing and printing environment. Additionally, it is highly desirable that this solution be obtained without physical modification to the printing device and without the need for costly special materials and media.
Watermarking is a common way to ensure security in digital documents. Many watermarking approaches exist with different trade-offs in cost, fragility, robustness, etc. One approach is to use ultra-violet (UV) ink rendering, to encode a watermark that is not visible under normal illumination, but revealed under UV illumination. The traditional approach, often used in currency notes, is to render a watermark with special ultra-violet (UV) fluorescent inks and to subsequently identify the presence or absence of the watermark in a proffered document using a standard UV lamp. One example of this approach may be found in U.S. Pat. No. 5,286,286 to Winnik et al., which is herein incorporated by reference in its entirety for its teachings. However, these inks are costly to employ, and thus are typically only economically viable in offset printing scenarios, and thus only truly avail themselves of long print runs. Additionally, these materials are often difficult to incorporate into standard electro-photographic or other non-impact printing systems like solid ink printers, either due to cost, availability or physical/chemical properties. This in turn discourages their use in variable data printing arrangements, such as for redeemable coupons, for but one example.
Another approach taken to provide a document for which copy control is provided by digital watermarking includes as an example U.S. Pat. No. 5,734,752 to Knox, where there is illustrated a method for generating watermarks in a digitally reproducible document which are substantially invisible when viewed including the steps of: (1) producing a first stochastic screen pattern suitable for reproducing a gray image on a document; (2) deriving at least one stochastic screen description that is related to said first pattern; (3) producing a document containing the first stochastic screen; (4) producing a second document containing one or more of the stochastic screens in combination, whereby upon placing the first and second document in superposition relationship to allow viewing of both documents together, correlation between the first stochastic pattern on each document occurs everywhere within the documents where the first screen is used, and correlation does not occur where the area where the derived stochastic screens occur and the image placed therein using the derived stochastic screens becomes visible.
For each of the above patents and citations the disclosures therein are totally incorporated herein by reference in their entirety.
Disclosed in embodiments herein is a fluorescent mark indicator comprising a substrate containing optical brightening agents and, a colorant layer deposited upon the substrate to create an image upon the substrate. The colorant layer has as characteristics a property of high suppression of substrate fluorescence, as well as a property of low contrast against the paper substrate under normal illumination, whereby the resultant substrate image suitably exposed to an ultra-violet light source, will yield a discernable pattern evident as a fluorescent mark.
Further disclosed in embodiments herein, is a fluorescent mark indicator comprising a paper substrate containing optical brightening agents, and a first colorant mixture printed as an image upon the paper substrate, the first colorant mixture providing a property of relatively high suppression of substrate fluorescence. The mark indicator further comprises a second colorant mixture printed as an image upon the paper substrate in substantially close spatial proximity to the printed first colorant mixture, the second colorant mixture providing a property of relatively low suppression of substrate fluorescence, and a property of low contrast against the first colorant mixture, such that the resultant colorant patterned paper substrate suitably exposed to an ultra-violet light source, will yield a discernable image evident as a fluorescent mark.
Further disclosed in embodiments herein, is a system for creating a fluorescence mark comprising a paper substrate containing optical brightening agents, and a digital color printing system. The digital color printing system further comprising at least one first colorant mixture that exhibits a property of high absorption of substrate fluorescence under ultra-violet light, and at least one second colorant mixture that exhibits a property of low absorption of substrate fluorescence under ultra-violet light as well as a property of low contrast as compared against the at least one first colorant mixture under normal illumination. The system further comprising a color image printed with the digital color printing system on the paper substrate, the color image comprising at least said first colorant mixture and said second colorant mixture arranged in close spatial proximity to each other, the spatial arrangement of the at least two colorant patterns revealing a fluorescence mark when the printed color image is viewed under ultraviolet light.